Cytokine-induced expression of ICAM-1 (Intercellular Adhesion Molecule-1, CD54) on the surface of epidermal keratinocytes is a prerequisite for leukocyte/keratinocyte attachment and immunologic cytotoxicity of keratinocytes. We have found that the epidermis is a stratified immunologic environment, especially with respect to ICAM-1 induction. We propose that the epidermal basal keratinocyte is particularly susceptible to immunologic cytotoxicity because of enhanced ICAM-1 induction by cytokines. In this grant we will focus on individual and differentiation-dependent variation in induction of ICAM-1 expression in keratinocytes. We will identify "high" and "low" responders to TNF-a and IFN-g by analysis of cell surface ICAM-1 expression and distribution by FACS and ELISA. We will determine if cultured keratinocytes from these donors show significant differences in cytokine receptor distribution, density or function, and whether these receptors can be induced by cytokine priming. We will also analyze the effects of keratinocyte differentiation on these receptor variables and on ICAM-1 MRNA induction using Northern and slot blot analysis. Individual and differentiation-dependent differences in release of TNF-a in keratinocytes will also be characterized by FACS, immunoblot and Northern blot analysis, to further characterize the high TNF-a responder phenotype. We will also determine if IL-1a is an inducer of ICAM-1 in basal keratinocytes and whether icIL-1ra is responsible for low IL-l responses in more differentiated keratinocytes. Finally, we will verify that enhanced ICAM-1 expression determines the level of immunologic cytotoxicity of keratinocyte targets. We will further test this hypothesis in a prototype of basal keratinocyte cytotoxicity: photosensitive lupus erythematosus. Using keratinocytes from lupus patients, we propose to show that TNF-a induction of expression of ICAM-1 and Ro/SSA or La/SSB antigens on the cell surface of keratinocytes renders these cells susceptible to cytotoxic damage by anti Ro/SSA or La/SSA antibodies and/or cellular effectors. These experiments address the control and functional significance of the stratified expression of the adhesion molecule ICAM-1 in the epidermis-a most critical step in keratinocyte cytotoxicity. This work is crucial in our long-term study of the cytotoxic mechanisms of skin diseases.